1. Field of the Invention
The present invention relates in general to internal combustion engines and more particularly to a piston of the type having a ceramic insert that covers a piston head portion defining a cavity that serves as a combustion chamber of an internal combustion engine.
2. Description of the Prior Art
A piston of the above described type is known in the art and exemplarily shown in FIG. 8. The known piston includes a ceramic insert (C) that is embedded or cast in a piston head (A) to entirely cover a piston head portion defining a cavity, i.e., to entirely cover the circumferential wall portion (B) and the bottom wall portion (D) of the cavity.
The insert (C) is embedded or cast in the piston body by installing the ceramic insert on a core and disposed in place in a casting die together with the core so that the ceramic insert (C) is cast in the piston body when the molten metal poured into the die solidifies.
The prior art piston of the above described kind has a disadvantage that in manufacture of the piston cracks, pinholes, a vacant space (E), etc. are liable to be caused in a cast piston body portion adjacent a central projection (F) in the bottom of the cavity due to the shrinkage of the cast metal, causing a stress differential between the piston body portion adjacent the central projection (F) and the remaining piston body portion and allowing the ceramic insert to be broken by the stress differential.